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Risk estimation for Down's syndrome and neural tube defects by analysis of triple test parameters in maternal serum 1999-2002

Risicoschatting voor Down syndroom en neuraalbuisdefecten door analyse van triple test parameters in maternaal serum 1999-2002


In this report we describe a survey of over 14,000 triple test requests to estimate risks for Down syndrome and neural tube defect (NTD) pregnancies. They were collected between 1999 and 2002, from all the provinces in the Netherlands except Groningen, Friesland and Drenthe. This research was carried out on order of the Health Care Inspectorate of the Dutch Ministry of Health, Welfare, and Sport. Pregnancies were classified as either normal singleton pregnancies or special (e.g. diabetic, twin) pregnancies. Experimental data of the triple test (alpha fetoprotein, unconjugated oestriol and human chorionic gonadotropin) for singleton normal pregnancies are given, with special reference to the age distribution of the population under investigation. The median values of the triple test parameters in Downs syndrome or neural tube defect-pregnancies are given, as well as the detection rate (DR) and false positive rate (FPR) of the triple test using reported data on the outcome of pregnancies. Special attention is given to e.g. the time a sample is in transport and the gestational age at which a blood sample is taken. Moreover, this report addresses in more detail the values of the triple test parameters in twin and diabetic pregnancies, and reports on individual cases of Down syndrome, neural tube defects and trisomy 18. The annual number of triple tests rose slightly in 2001 and 2002 to annually about 3700. No significant changes were found in the categories of requestors (e.g. hospital vs. obstetricians), regional distribution, and the median age at which women applied for a triple test. The distribution of multiple-of-the-median values for the triple test parameters were within the demands of the triple test risk estimation. A report of the outcome of the pregnancy was received for 79% of all the triple tests in 1999 and for 84% of the tests in 2000-March 2001. Based on these data, the DR for Down syndrome was 90% for a 15,6% FPR in 1999 and 80% for a 15,6% FPR in 2000-March 2001. The DR for NTD was 50% for a 0,8% FPR in 1999 and 0 % for a 1.2% FPR in 2000-March 2001 (however, in both periods only 2 NTD-pregnancies were reported). These specifications meet or exceed minimum demands for detection and false positive rates, as estimated from the age distribution of the pregnant women, except for the detection rate of NTD, which is lower then expected.

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